This invention relates in general to a safety system, and more particularly to an accurate and reliable safety system for a gas sterilization facility which prevents a person from opening the chambers in the facility if dangerous levels of gas are present in the chambers.
Gas sterilization facilities exist throughout the world. These sterilization facilities are used to sterilize a variety of articles such as medical devices, surgical instruments and other healthcare supplies and equipment. The sterilization process used to sterilize these articles must completely kill or destroy the microorganisms on these articles.
Ethylene oxide sterilization is a widely used, effective method for sterilizing such articles. Ethylene oxide gas is an extremely effective bactericide for metal objects, such as surgical implements, as well as relatively delicate instruments and equipment including synthetics or plastics. Moreover, since ethylene oxide gas is effective at relatively cool temperatures, the ethylene oxide sterilization process does not employ high temperatures which can degrade articles made of certain materials. Ethylene oxide gas also penetrates certain packaging materials and is therefore effective in sterilizing articles in appropriately designed packages. Ethylene oxide sterilization is preformed on a large scale at sterilization facilities having multiple industrial size sterilization chambers and on a smaller scale at facilities, such as hospitals, which typically have one or relatively few, smaller sterilization chambers. During the ethylene oxide sterilization process, the packaged articles to be sterilized are placed in a sterilization chamber, the door of the chamber is closed, sealed and locked and a process is initiated including drawing a vacuum and sometimes injecting steam in the chamber. Ethylene oxide gas is then introduced into the sterilization chamber for a period of time sufficient to sterilize the articles in the sterilization chamber.
During the sterilization process, certain amounts of the ethylene oxide gas are physically absorbed into the articles undergoing sterilization. After the articles are exposed to certain levels of ethylene oxide gas for a period of time, the ethylene oxide gas in the sterilization chamber (which is not absorbed into the articles) is exhausted or flushed from the chamber. However, the ethylene oxide gas which was absorbed by the articles is not immediately removed from the sterilization chamber. The ethylene oxide gas absorbed by the articles is slowly xe2x80x9cdesorbedxe2x80x9d from the articles back into the sterilization chamber. As the ethylene oxide gas is desorbed from the articles into the sterilization chamber, the desorbed ethylene oxide gas may be exhausted or flushed from the sterilization chamber. However, since desorption occurs over an extended period of time and is an irregular uncontrolled process, even after the sterilization chamber has been exhausted or flushed multiple times, the atmosphere in the sterilization chamber will most likely still contain ethylene oxide gas desorbed from the articles, subsequent to the last exhausting or flushing cycle for the chamber. Even though the amount of ethylene oxide gas that is in the articles can be measured, it is difficult to know when and at what rate the ethylene oxide gas will be desorbed from articles into the sterilization chamber. The sterilization chamber thereby includes a vent exhaust system which is automatically triggered when the door of the chamber is slightly opened. The vent exhaust system directs the vented gas from the chamber to emission control equipment which may include one or more ignition sources.
Ethylene oxide gas is toxic to human beings, flammable and potentially explosive. If the door of a sterilization chamber is opened when a certain level of ethylene oxide gas is present in the chamber (i) due to incomplete exhausting or flushing of the chamber, (ii) after additional ethylene oxide gas is released into the sterilization chamber due to the continued desorption process, (iii) at the wrong time during the sterilization cycle, or (iv) after there has been an unknown equipment or control malfunction, the gas mixture in the vent exhaust system and chamber could be flammable and have the potential to ignite causing an explosion to occur as a result of the explosive gas mixture coming into contact with any of several potential ignition sources. Also, the person opening the chamber or the other people in the sterilization facility could be exposed to the toxic ethylene oxide gas. This creates a potentially dangerous environment for the personnel operating the sterilization facility, especially since the desorption process is irregular and uncontrolled.
For safety purposes, strict procedures must be followed while opening the door to any sterilization chamber. These procedures include creating sufficient vacuum draw downs of the gas in the chamber, followed by a gas in-bleed of air or nitrogen (i.e., gas washes) which removes much of the ethylene oxide gas from the articles and packaging in the chamber. Thereafter, the door of the chamber is slightly opened, which triggers the back vent or vent exhaust system. The back vent draws air into the chamber through the opening between the door and the door frame, to flush out the empty chamber space surrounding the articles and packaging. After a predetermined period, the chamber door may be fully opened to remove the articles and packaging in the sterilization chamber. These procedures may not be followed due to human error, equipment failure or control system failure. Accordingly, there is a need for accurate and reliable safety systems in gas sterilization facilities, and particularly in ethylene oxide sterilization facilities, to measure the level of ethylene oxide gas in the sterilization chamber and to prevent opening of the door to the sterilization chamber if the level of ethylene oxide in the chamber is above a predetermined level.
Microwave spectrometers are generally known for detecting the presence and concentration of ethylene oxide gas and other gases. For example, U.S. Pat. Nos. 5,209,902, 5,399,314 and 5,548,217 disclose the use of microwave spectrometers for detecting the presence and concentration of ethylene oxide gas. Microwave spectrometers have also been employed to measure the concentration of ethylene oxide gas in a sterilization chamber to facilitate parametric release of the articles. For example, Griffith Micro Science, Inc. currently uses microwave spectrometers to facilitate parametric release on a limited number of ethylene oxide sterilization chambers. The microwave spectrometer used by Griffith Micro Science, Inc. is generally described in the publication entitled Specificity, Accuracy, And Interpretation Of Measurements Of Ethylene Oxide Gas Concentrations During Sterilization Using A Microwave Spectrometer published in the Rev. Sci. Instrum. (68) 7, July 1997. No known ethylene oxide sterilization facility, however utilizes a microwave spectrometer in a reliable and accurate safety system which prevents access to the sterilization chambers based on the concentration of ethylene oxide gas in the sterilization chambers.
Accordingly, there is a need for an accurate and reliable safety system or other apparatus or method to determine whether it is safe to unlock the door of a sterilization chamber, and in particular an ethylene oxide sterilization chamber, based on the measured concentration of sterilization gas in the sterilization chamber regardless of whether those levels are due to continuing desorption of the sterilization gas from the articles and packaging into the sterilization chamber, human error or equipment or control system malfunction. The desired safety system must prevent the opening of a sterilization chamber when a dangerous level of sterilization gas is present in the sterilization chamber.
The present invention solves the above problems by providing an accurate and reliable safety system for a gas sterilization facility having one or more sterilization chambers, and in particular, for an ethylene oxide sterilization facility having one or more ethylene oxide sterilization chambers. The safety system of the present invention is adapted to determine if the concentration of ethylene oxide gas in each sterilization chamber is above or below a predetermined level, determines whether it is safe to unlock the door of each sterilization chamber based on the concentration of ethylene oxide gas in the sterilization chamber, limits access to the sterilization chambers if dangerous levels of ethylene oxide gas are present in the sterilization due to the possible continued desorption of the ethylene oxide gas from the articles into the sterilization chambers, and limits the possible effects of human error or equipment or control system malfunction. The present invention thereby improves the overall safety at ethylene oxide sterilization facilities. A sterilization facility having one or more sterilization chambers may have a separate safety system associated with each sterilization chamber, or more preferably, will have a single safety system associated with all of the sterilization chambers in a sterilization facility or a section of the sterilization facility. The safety system will preferably have a dedicated gas measuring apparatus or microwave spectrometer connected to all of the sterilization chambers. The dedicated microwave spectrometer will not be used for facilitating parametric release of the articles. It will be appreciated that the safety system of the present invention could be employed in alternative gas sterilization systems and could be employed in the other types of gas process systems or facilities to measure dangerous levels of specified gases and to limit access to areas based upon such measurements.
The safety system of the present invention generally includes a central processing unit, a master control panel, a chamber control panel on each sterilization chamber, an electropneumatically activated locking mechanism for the door of each sterilization chamber, a gas measuring apparatus such as a microwave spectrometer, a chamber sample valve for each sterilization chamber and a pump connected to the chamber sample valves and the gas measuring apparatus. An operator in the sterilization facility operates the safety system of the present invention through the master control panel or the chamber control panels. The central processing unit controls the operation of the safety system, including the door locking mechanisms, the control panels, the chamber sample valves, the pump and the gas measuring apparatus. The central processing unit may also communicate using electric lines to the computer control system of the sterilization facility. The locking mechanism on the door of each sterilization chamber is adapted to lock and unlock the door upon commands from the central processing unit. The pump and the chamber sample valves are adapted to obtain gas samples from the sterilization chambers upon commands from the central processing unit. The gas measuring apparatus is adapted to determine the presence and the concentration of a specified gas in the gas samples obtained from the sterilization chambers. Gas communication lines or pipes connect the chamber sample valves, the pump and the gas measuring apparatus.
The safety system of the present invention prevents an accidental or inadvertent opening of the doors of the sterilization chambers. After a door of a sterilization chamber is closed and the sterilization cycle begins, the door is locked and the safety system prevents the door from being unlocked until the safety system samples the atmosphere in the sterilization chamber and determines that it is safe for the door to be opened. To unlock the door, an operator in the sterilization facility directs the central processing unit through the master control panel or the chamber control panel of a sterilization chamber to determine if the concentration of ethylene oxide gas in the specified sterilization chamber is above or below a predetermined level. The central processing unit sends a signal to the chamber sample valve of the sterilization chamber to obtain one or more gas samples from the sterilization chamber. The gas samples are directed through the connecting tubes and pump to the gas measuring apparatus. The gas measuring apparatus determines if the concentration of ethylene oxide gas in the gas samples is above a predetermined level. This sampling and measurement process is preferably repeated multiple times to obtain reliable measurements. The gas measuring apparatus sends a signal to the central processing unit as to whether the level of ethylene oxide gas in the gas samples taken from the sterilization chamber is safe or unsafe.
If the level of ethylene oxide gas in the sterilization chamber is unsafe or above a predetermined level, the central processing unit will not unlock the door and will provide a message to the operator via the master control panel and the chamber control panel indicating that there is an unsafe level of ethylene oxide gas in the sterilization chamber. The sterilization chamber may then be further exhausted or flushed. An additional period of time may be required to allow for further flushing of the desorbed ethylene oxide gas. The sampling and measurement process preformed by the safety system will need to be repeated before the door is opened.
If the level of ethylene oxide gas in the sterilization chamber is safe or below a predetermined level, the central processing unit will send a signal to the locking mechanism of the sterilization chamber to unlock the door of the sterilization chamber. The central processing unit will also provide a message to the operator via the chamber control panel and the master control panel that the door is unlocked. The door of the sterilization chamber may then be opened to provide access to the sterilization chamber and to remove the articles which have undergone sterilization.
After the initial measurement is made, the level of ethylene oxide gas in the sterilization chamber could increase to dangerous levels due to the continued desorption of the ethylene oxide gas from the articles in the chamber which may occur at uneven rates. To avoid such potential problems, if the door of the sterilization chamber is not opened after a predetermined period of time, the central processing unit will send a signal to the locking mechanism to re-lock the door of the sterilization chamber, thereby preventing access to the sterilization chamber until further safe measurements are made. The central processing unit will also send a message to the chamber control panel and the master control panels that the door is locked.
The safety system of the present invention employs a microwave spectrometer to reliably and accurately measure the concentration of ethylene oxide gas in the gas samples taken from the sterilization chambers. The microwave spectrometer of the present invention is suitably calibrated to accurately and reliably measure relatively low concentrations of ethylene oxide gas in gas samples. The microwave spectrometer is therefore preferably employed in the safety system, although it should be appreciated that alternative gas measuring apparatus such as infrared, near infra-red, gas chromatographs or other accurate and reliable measuring apparatus could be employed in the safety system of the present invention if they are adjusted or calibrated to accurately and reliably measure such relatively low concentrations of ethylene oxide gas in the sterilization chambers. The safety system of the present invention preferably includes a single dedicated microwave spectrometer for multiple sterilization chambers in a sterilization plant or facility. The gas samples taken from each sterilization chamber are directed to the single microwave spectrometer. One or more back-up microwave spectrometers could also be employed in the safety system of the present invention to enable the safety system to continue to operate if the primary microwave spectrometer malfunctions. A single microwave spectrometer could be connected to each sterilization chamber; however, the use of multiple microwave spectrometers would dramatically increase the cost of the safety system, unnecessarily complicate the safety system and increase the possibilities for malfunction of the safety system.
It is therefore an object of the present invention to provide a safety system for a sterilization facility.
Another object of the present invention is to provide a safety system for a gas sterilization facility having one or more sterilization chambers.
Another object of the present invention is to provide a safety system for a gas sterilization facility which determines if the concentration of sterilization gas in gas samples obtained from a sterilization chamber is above a predetermined level, and prevents access to the sterilization chamber if the level of sterilization gas in the sterilization chamber is unsafe.
A further object of the present invention is to provide a safety system for a sterilization facility which limits access to a plurality of sterilization chambers and minimizes serious consequences as a result of human error or equipment or control system malfunction.
A yet further object of the present invention is to provide a safety system which unlocks the door of the sterilization chamber if the level of sterilization gas in the sterilization chamber is below a predetermined level.
A still further object of the present invention is to provide a safety system for a sterilization facility which determined the concentration of a specified gas in one or more gas samples taken from a sterilization chamber to ensure a reliable measurement.
A yet further object of the present invention is to provide a safety system for a sterilization facility which unlocks the door of a sterilization chamber if the level of sterilization gas in the sterilization chamber is below a predetermined level and relocks the door if the door is not opened after a predetermined period of time.
Other objects, features and advantages of the present invention will be apparent from the following detailed disclosure in conjunction with the accompanying sheets of drawings, wherein like reference numerals refer to like parts.